Pharmacologically relevant concentrations of benzodiazepines have previously been reported to increase 45Ca2+ uptake into synaptosomes. This observation, coupled with the recent report that nifedipine may block the hypnotic effect of flurazepam, led us to study the effects of nifedipine and nitrendipine on 45Ca2+ uptake into synaptosomes. Both agents had little effect by themselves, but prevented enhancement of uptake by diazepam. These observations further support the notion that benzodiazepine receptors in brain may be coupled to a calcium channel which may have some relevance to the actions of benzodiazepines.